1. Field of the Invention
One embodiment of the present invention relates to a semiconductor device and a manufacturing method thereof.
Note that a semiconductor device refers to a device which can function by utilizing semiconductor characteristics; an electro-optical device, a semiconductor circuit, and an electronic appliance are all included in the category of the semiconductor device.
2. Description of the Related Art
In the case of forming a thin film transistor (hereinafter also simply referred to as a transistor) which is used for a semiconductor device, an insulating layer formed using a silicon oxide film, a silicon nitride film, or the like is provided over the thin film transistor so as to prevent corrosion of a wiring portion and change in electrical characteristics of the thin film transistor which are caused by permeation of external moisture (for example, see Patent Document 1).
Note that “moisture” in this specification is used as a generic term covering water, water vapor, water molecules, hydrogen molecules, and hydrogen atoms. Note that the expression “moisture permeability is low,” for example, is construed that “permeability to one or more of water, water vapor, water molecules, hydrogen molecules, and hydrogen atoms is low.”